The present invention related to a nucleus to be inserted into shellfish at the cultivation of the cultured pearl.
It is well-known that, when a particle of solid such as sand or others is inserted into the specific kind of shellfish, a small grain of pearl is produced naturally. However, the production of natural pearl is uncertain, and the size of an obtained natural pearl is not so large and also the shape of it is indefinite. About one hundred years ago, the technique to culture a pearl by inserting a nucleus artificially into a mother shellfish such as pearl oyster, white-lip pearl oyster, black-lip pearl oyster, penguin wing oyster, abalone, hyriopsis schlegel, mussel, anodonta woodiana, or fresh water pearl mussel was developed in Japan. This technique is gradually improved, and now it becomes possible to culture a large size pearl certainly. Recently, almost 100% of ornamental pearls are produced by said culture technique.
However, recently, the environment surrounding an aqua farm for cultivation are gradually becoming worse, and by the conventional culture technique, the breeding of mother shellfish for several years after inserting of nucleus becomes very difficult. Further, by the affect of breeding environmental pollution, survival ratio of mother shellfish is remarkably deteriorated.
The object of the present invention is to improve the yield of large size pearl and to reduce the ratio of death of mother shellfishes.
The inventors of the present invention have found that above mentioned problems can be solved by the use of a coated nucleus for a cultured pearl whose surface is coated with water soluble polymer, characterizing over 25% of total coated amount of said water soluble polymer is dissolved by soaking said coated nucleus into seawater of 15xc2x0 C. temperature for 30 minutes, and accomplished the present invention.
By the use of a coated nucleus of this invention, when said coated nucleus is inserted into a mother shellfish, the load to the mother shellfish can be reduced, because water soluble polymer that coats a nucleus is partially dissolved and the friction and resistance at the inserting action is weakened. Consequently, the yield of large size pearl can be improved, and the ratio of death of mother shellfishes can be reduced. Further, the present invention contains a substance that has antibacterial activity as a part of coating component. Said substance having antibacterial activity dissolves together with a coating material and acts to an incised part of the mother shellfish to insert the coated nucleus and prevent the infection due to said antibacterial activity. Thus, the coated nucleus of this invention can further reduce the ratio of death of mother shellfishes.
The important point of a coated nucleus for a cultured pearl of this invention is illustrated in detail as follows.
That is, the coated nucleus of this invention is a nucleus for culture whose surface is coated by water soluble polymer, and after coated, it is necessary that over 25% of total coating amount of said water soluble polymer is dissolved when placed in the seawater of 15xc2x0 C. temperature, that is a culture condition of a mother shellfish, for 30 minutes. The solubility of the coated polymer depends on a kind of coated material, coating amount and a coating method. However, in any case it is necessary that over 25% of total coating amount is dissolved, and if the dissolving ratio is under 25%, the reduction of the friction and resistance at the inserting action is not sufficient.
As the water soluble polymer, although any kinds of natural or synthetic polymer can be used, especially, natural water soluble polymer is desirably used. As the natural polymer, protein, polysaccaride or lipid can be mentioned. As the concrete example, collagen, gelatin, casein, albumin, elastin, alginic acid, pectin, arabic gum, carrageenan, xanthane gum, pullulan, starch or derivatives of these compound for example, succinyl collagen, methyl collagen, acetyl collagen, phthalic collagen, succinyl gelatin, methyl gelatin, acetyl gelatin, phthalic gelatin, carboxymethyl starch, methylhydroxy starch, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose can be mentioned. Still more, synthetic water soluble polymer can be used, and concretely, polyvinyl alcohol, polyvinyl pyrrolidone, carboxyvinyl polymer, polyacrylic acid and salt thereof, polyacrylamide, polyethylene glycol and these derivatives can be mentioned. And, the combination of these compounds, concretely mixed solution of these compounds is used. After coating a layer, another layer can be coated over the layer. Thus the multiple layers can be prepared by coating a layer one by one.
The substance that has antibacterial activity can also be contained in a coating layer. As the substance having antibacterial activity, any kinds of substance that has antibacterial activity including bacteria controlling activity can be used and not restricted. Concretely, an antibiotic, a silver containing compound, a preservative or a conservative can be mentioned, and especially an antibiotic is desirably used. As the concrete examples, tetracycline, tetracycline hydrochloride, kanamycin, sulfamonomethoxyne, sodium salt of sulfamonomethoxyne or ampicillin, which are ordinary antibiotic in the marine products industries can be mentioned. Necessary amount to be added to a coating layer of each substance having antibacterial activity are depending to the intensity of it""s antibacterial activity, therefore, the concrete amount to be added is not definite, however, in a case of antibiotic, the desirable amount to be added is 0.1-20 times to the amount of coated material.
In this invention, a method for coating is not restricted, and whole surface of a nucleus can be coated homogeneously or partially. As the concrete coating method, for example, following methods can be mentioned. A method to soak a nucleus into the solution containing coating materials then dried up, or a method to spray the solution containing coating materials over the surface of a nucleus then dried up can be mentioned. Actually, a coating apparatus which is on the market (for example, HIGH COATER; product of Froint Industries Co., Ltd.) can be used.
The concentration, pH or temperature of aqueous solution of water soluble polymer is not restricted. However, in regard to the concentration, the viscosity of solution affects largely the coating process and when the viscosity is too high, the coating becomes very difficult. Concretely, it is necessary for the coating solution to have a viscosity as measured by following method. That is, when a container containing said coating solution is inclined, contained solution which has adequate viscosity must be flown along with the motion of the container.
pH value of the aqueous solution of water soluble polymer used for the coating of this invention is also not restricted. In general, as a nucleus to be inserted into mother shellfish, a small grain cut from a shell of shellfish then processed is used, whose main component is calcium carbonate. Therefore, if the pH value of the solution is smaller than 1, it is not desirable because the nucleus can be dissolved in the solution. And when the nucleus is inserted in the mother shellfish, pH of the inserted nucleus becomes same to the body fluid of the shellfish because the body of shellfish surrounds it. In a case, if a water soluble polymer which has strong electric charge is used, it is desirable to use the solution whose pH is near the neutral range.
The temperature of the solution is not restricted as long as the temperature affects the nucleus. And, it is possible to raise the temperature of solution to reduce the viscosity, or to expedite the drying. According to the kind of water soluble polymer, sometimes the temperature of solution is restricted. Actually, it is necessary to adjust the temperature of solution in the limit in which contained water soluble polymer is not denatured or decomposed by the effect of the temperature. Further, it is possible to add the component which does not give any effects to the mother shellfish.
The coated amount of water soluble polymer is not restricted, however, if the coating amount is too small, the sufficient effect can not be expected. And if the coated amount is too much, the inserting action of a nucleus becomes difficult because of high viscosity of water soluble polymer. Concretely, it is desirable that the coated part of a nucleus is bigger than 30% of the total surface area of a nucleus and the thickness of most thick part of coated layer is thinner than 1 mm.
As the kinds of material to be coated, one kind of water soluble polymer can be used alone or various kinds of water soluble polymer can be used together with. Further, after the first layer is coated, another layer composed of different kind of water soluble polymer can be accumulated.